Nutating back pad



June 22, 1954 B. Toccl-GUILBERT l 2,681,532

NUATATING BACK PAD Filed April l6. 1955 Patented June 22, 1954 NUTATING` BACK PAD Berne Tocci-Guilbert, San Francisco, Calif., as-

signor to Berne Tocci-Guilbert, San Francisco, and Henry Gifford Hardy, Berkeley, Calif.,

jointly, as trustees Application April 16, 1953, Serial No. 349,247

3 Claims.

The invention relates to improvements in back pads for use in connection with grinding or sanding discs, bufiing pads, and the like, which are normally attached to sanding and polishing machines, and particularly the invention is directed to aback pad which will provide an oscillatory movement especially when applied to the work for at grinding, sanding or polishing and which will also absorb axial distortion and strain on the shaft and bearings of the grinding machine, whenapplied to the work at a point near its periphery, spaced from the axis of the drive shaft.

The invention contemplates the employment of features formerly obtainable only with the addition of a special piece of equipment known as an oscillator used in conjunction with the usual back pad construction, wherein the beneficial results of both pieces of equipment are combined in a single unit without extending the length of the drive shaft and increasing the distance to the Work.

In general, an embodiment of the present invention employs the usual resilient, flexible back pad but in this invention it is countersunk at its central portion and reinforced thereat with a fully bonded top plate to receive and hold the sanding and grinding disc with suitable resilience and flexibility toward the periphery. The bottom plate and the collar, by which the device is attached to the shaft of a power tool, are joined together and, as a unit, are bonded to the main resilient body, preferably with the internal edge of the collar member axially embedded in the body material to key this unit in position. It will be observed that the bottom plate and collar assembly is spaced from the top plate by the mass of resilient material, but any tendency to have the resilient material shear transversely due to a sudden difference in torque is prevented and minimized by having the flare of the base plate extend axially to a point beyond any possible shear point of the body. y

It is an object ofthe present invention to provide a back pad which in and of itself will absorb any axial misalignment during rapid rotation when only a small portion of the periphery is applied to the work.

It is likewise an object of the present invention to provide a resilient back pad which will permit high speed grinding, sanding, polishing or like operation with the axis of the drive shaft substan-` tially at right angles to the plane of the work surface.

It is also an object of the present invention to provide a resilient bac-k pad which combines an oscillator with the normal resilient or flexible back pad without in any way increasing the length of the shaft, thus permittingf surface grinding or other treatment of large, dat or curved surfaces without `concentric greoving, hill and cutting or the other deleterious results normally incident to such work, especially when done at high speeds.

A further object of the invention is to furnish a back pad with free oating mo-tion which, in conjunction with appropriate abrasives, will accomplish very :line finishes (lap grinding and polishing) with very low abrasive pressures and with no tendency to walk, dig or make 4concentric rings.

lt is a further object of the present invention to provide a back pad for grinding, polishing and buiiing purposes which will not only have the necessary rigidity for applying force to the disc face at the point of work, but which at the same time will minimize the axial distortion of the power shaft connected to the driving mechanism` Still another object is to supply a combined oscillating back pad wherein the resilient portions are never in direct shearing relation.

Another object of this invention is to provide a back pad which will operate successfully :in sanding, grinding, polishing and like operations at peripheral pressures greater than now used without transmitting axial distortion and misalignment to the operating shaft.

Further objects are to provide a construction of maximum simplicity and economy of production, also such further objects, advantages and capabilities as will fully appear and as are inherently possessed by the device and invention disclosed herein.

The invention further resides in the combination, construction and arrangement of parts illustrated in the accompanying drawings, and while there is shown therein a preferred embodiment and several modiiications, it is understood that the same are merely illustrative of the invention, and that the invention is capable of modiiication and change and contemplates such other details of construction without departing from the spirit thereof or the scope of the appended claims.

Referring to the drawings:

Figure l is a top plan View of the structure of the present invention attached to a spindle shaft, with an abrasive disc in place.

Figure 2 is a vertical section taken on the line lli-II of Figure l.

Referring now to Figures 1 and 2 of the drawings, in which like reference numerals are used to designate the same parts in the two views, and with particular reference to Figure 2, the nutat ing back pad of the present invention is shown in vertical section as a unit attached to a spindle shaft and carrying a selected abrasive disc. It is 'to be understood that the spindle shaft and the abrasive disc are not part of the structural combination of the invention but are shown merely to the escription. The back pad of this invention is a complete, integral unit ready to be attached to the shaft of any suitable machin@ or tool. It is not assembled on the shaft when desired for use. The main body portion lo of the back pad is preferably rubber, either natural or synthetic, which is molded with and bonded to the other members of which it forms an integral part. It is to be understood that the main body portion It may be made from any suitable resilient or flexible material. The outer surface or face i I of the body I is dished at its central portion and reinforced with an inwardly sloping grommet or top plate I2 which is molded with and bonded to the body IU. The top plate I2 has a threaded axial bore I4 to receive the retaining nut I5.

The bottom plate I6 is cup-like in shape and is used in inverted position. The side wall il flares outwardly as it extends downwardly and axially along the outer surface of the back pad, until it reaches a point laterally beyond the inner Vterminus of the top plate I2. A collar i8 extends through the plate IE coaxially with the body i8, the top plate i2 and the bottoni plate it. The collar I 8 is the coupling member for attachment of the back pad to a tool, and may be internally threaded as at I9 for attachment to the threaded end of a spindle shaft 2d, or any other shaft providing rotary movement. The threaded engagement with the shaft 2!) is merely optional as the collar may be adapted to t any other form or means required to attach the device to a rotating shaft.

The coupling collar I8 is preferably made with an outwardly ilared inner terminus 2i. Both the bottom plate and the coupling collar i8 may be made from stampings and are brazed or otherwise rnaole integral at their juncture 22, to make them respond as a single piece.

In making the back pad the several parts, i. e., the bottom plate I6 and its joined coupling collar i8, the material forming the body is and the top plate E2 are placed in a mold and subjected to both heat and pressure. The result is that all of these members are molded and bonded together to provide a complete unitary structure ready for use and attachment to the shaft of any suitable tool. It will be observed that the outwardly ilared terminus 2l `of the coupling collar i3 serves to key the assembly to the molded rubber body portion lil.

Figure 2 of the drawings shows an area 23 inV phantom lines. Preferably, the resilient material forming the body Ed fills this area 23, as well as the remainder, stances the back pad is secured to the end of the shaft by means of a screw and lock washer (not shown). Accordingly, the area 23 has to be leit clear se the head of the screw may be reached by a screw driver passing up through the central aperture of the retaining nut I5. In addition, the resilient material forming the body Ed may be made in any degree of hardness or softness desired, or it may be formed as a composite body comprising a softer inner portion lila and a harder cuter portion i919, or vice versa.

The retaining nut i is preferably made with an axial passage 24 therethrough, which passage is preferably square or hexagonal to accommodate a wrench.

As shown in Figure 2, the face H and the Vgrommet or top plate I2 support an abrasive disc The abrasive disc is held onto the face by means of the retaining nut I. Although the back pad is illustrated in Figure 2 with an abrasive disc 25 attached, it may also be used for builing and polishing. Todo this, the operator removes the retaining nut i5 and the abrasive disc 25, and places the usual wool or sheepskin bonnet over the face II thereof.

However, in some in- As is shown in the prior art, back pad supports have been made for direct attachment to the motor shaft of sanding and polishing machines,

many of which are portable tools. This means that the drive of the back pad is directly coupled to the shaft of the motor. The speed of rotation required for operation is usually from 1560 to 3000 R. P. M. and at such speeds, only the peripheral portion of the grinding disc is, or can be used. Thus, only about the outer 1%; of an inch on the radius of the grinding or sanding disc is useful. In order to use the tool it is tilted at an angle with respect to the work so that the leading edge of the disc is in contact with the work and the trailing edge lifted, or the work is so placed that the tool can be used at an angle thereto, with only a small portion of the periphery contacting the work. it is not possible to use the full face of the grinding disc in such devices because the torsional friction is so great as to either stall the motor or jerk the tool from the operators grasp. It is to be noted that only the peripheral edge of the sanding or grinding disc is used whether a curved or dat surface is being worked upon and because of the requirements of use only a small portion of this area is in contact with the work atany one moment. All of this being true, it is easily understood that the point of application of the sanding disc to the work is spaced several inches from the motor shaft during operation. As pressure is applied against the work in order to accomplish sanding or grinding operation, the peripheral edge of the back pad fiexes at the point of contact and this further distorts and aggravates axial distortion.

The axial distortion between the point ci work contact and the axis of rotation when rigedly connected back pads are used, is transmitted to the bearings for the shaft and imposes a strain upon the motor, causing excessive bearing wear and loss of valuable time for necessary and frequent repair. Furthermore, concentric rotation under such circumstances makes it diiicult for the operator to hold the tool in proper position for continued work. Every bit of the jar and vibration of operation is transmitted from the tool to the hands, arms and shoulders of the operator, bringing on discomfort and early fatigue because of the direct coupling between the back pad and the tool shaft.

The nutating back pad of the present invention is speciiically responsible for a new typeV of grinding, which is at grinding or lap grinding, where the whole face or area of the abrasive disc may be placed against the work, if the piece is dat, without any danger of scoring, concentric grinding rings, burns, digging, or any of the other disadvantages which have made ilat grinding or lap grinding impossible with back pads in the prior art. Also, in cases where curved surfaces are used, or where ii; is desired to use the peripheral edge, the flexing of the pad at the point of work, causing axial distortion, will be taken up and minimized by the action of the plates against the resilient body, and not transmitted to the spindle shaft 2Q. Neither will the jars and vibrations of the work be transmitted to the person of the operator. Assuming there is a work pressure exerted at point A, Figure 2, which would normally cause axial misalignment of a line perpendicularto the face II and the axis of the spindle shaft 2e, the pressure is transmitted all Valong the right side of the device, as shown in Figure 2, causing the top plate I2 to compress the resilient material between it and the bottom plate IE and its wall Il'. This force is in turn transferred to the left side and the resiliency permits an expansion between the corresponding areas on the left side. Thus, the axial distortion or axial misalignment due to the offset Work pressure is not transmitted to the shaft 20, hence to the bearings and motor of the tool.

The interposition of the resilient body material I0 of the backing pad between the rigid coupling of the drive shaft with the bottom plate I6 and the driven top plate I2, results in a resilient cushioned coupling with no metal to metal contact between the driving and driven members. In operation this sets up a vibratory oscillating torque which makes possible full face flat; grinding, sanding, polishing, or like objective. Because there is no direct coupling between the spindle shaft 20 and the top plate I2, to which the abrasive disc is attached, and because the internal faces of the top plate, the bottom plate and the `flange coupling collar oppose each other and work against the resilient body l, a nutative movement is established so that the face of the abrasive disc I2 does not travel in a fixed orbit nor does it rotate concentrically with the axis of rotation of the spindle shaft 2t. Likewise, since it is quite impossible to apply equal full face pressures during operation, an oscillatory movement is also set up during operation. All of this causes a buing or rubbing action which breaks the concentric lines of rotation of the abrasive when working pressure is applied. The greater the pressure which is applied to the work, the greater the deviation and eccentricity resulting in an oscillating orbit Which makes it impossible to form concentric scoring lines in the surface being worked upon. The absence of concentric grinding torque prevents burning and deep scoring of any surface, as well as the elimination of buffing rings. Flat grinding, sanding and the like is essentially not possible without the oscillatory action provided herein. The frictional torque is either greater than the operator can hold when pressure is applied to the work or else it stops the motor. Likewise, in the absence of the oscillatory action, the abraded material, especially if the device is attempted for use on marble, cork,

rubber, or other soft surfaces, remains under the I placement. With the oscillatory movement provided for herein, it is possible to apply pressure to such soft materials and the abrasive is never lled or fouled because the movement constantly throws the abraded material to the outside and from under the working area. It is axiomatic that full face grinding and sanding permits an operator to cover many times the number of square feet of surface in a given period of time than was possible with peripheral grinding where only a small fraction of the area is ever in contact with the working surface.

It will be observed that any tendency for the resilient material of the body I 0 to shear laterally at any point above the inner terminus of the threaded portion of top plate I2 (which is the only area at which any tendency to shear has ever been noted), is prevented by the reinforcement established by the wall I7 of the bottom plate I6, extending axially beyond this point.

It is to be understood that the present invention is adapted for and equally eifective whether attached to a portable tool or to stationary grinding and finishing machines.

This present application is a continuation-inpart of my application Serial No. 149,138, filed March 11, 1950.

I claim:

1. Polishing and abrading apparatus of the character described, comprising a body of resilient material having a substantially frustoconical shape with a flared base, a top plate fixed to the base of said body to provide an abutment for an abrasive dise or the like, a bottom plate separated and spaced upwardly from said top plate by said resilient material, said plates being arranged concentrically to said body, said plates and said body being an integral unit complete and ready for attachment, and collar means secured to said bottom plate and keyed to said resilient material for coupling a shaft to said bottom plate only to rotate the apparatus about the common axis of said plates and body.

2. Polishing and abrading apparatus of the character described, comprising a body of rubber having a substantially frusto-conical shape with a flared base, a top plate having an inner flanged hub, fixed to the base of said body to provide an abutment and retention for an abrasive disc or the like, a bottom plate separated and spaced upwardly from said top plate having a depending wall extending axially beyond said flanged hub, said plates being arranged concentrically to said body and formed into an integral unit complete and ready for attachment, and collar means secured to said bottom plate for coupling a shaft to said bottom plate only to rotate the apparatus about `the common axis of said plates and body.

3. Polishing and abrading apparatus of the character described, comprising a body of resilient material having a substantially frustoconical shape with a ared base, a top plate having an inner flanged hub xed to the base of said body to provide a secure abutment for an abrasive disc or the like, a cup-like bottom plate having a depending wall forming a partial casing spaced upwardly and separated from said top plate by said resilient material, said plates beine,r arranged concentrically to said body and integral therewith to form a single unit ready for attachment, means for clamping a sanding disc or the like to said top plate concentrically thereof but without in any way contacting said bottom plate, and collar means secured to said bottom plate and keyed in said resilient" material for coupling a shaft to rotate the apparatus about the common axis of said plates and body.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,617,838 Fennell Feb. 15, 1927 1,725,361 Mall Aug. 20, 1929 1,779,682 Stratford Oct. 28, 1930 1,938,493 Myers Dec. 5, I1933 2,022,759 Delano Dec. 3. 1935 2,097,806 Wedrich Nov. 2, 1937 2,114,967 Myers Apr. 9, 1938 2,172,407 Rainey Sept. 12, 1939 2,337,588 Kemp Jan. 7, 1941 2,281,722 Smith May 5, 1942 2,439,751 Olsen Apr. 13, 1948 FOREIGN PATENTS Number Country Date 856,480 France Mar. 23, 1940 

